CVE-2021-21320
User content sandbox can be confused into opening arbitrary documents
matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- Low
- User interaction
- Required
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
User content sandbox can be confused into opening arbitrary documents
matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.
- Record
CVE-2021-21320- CVSS 3.1
- 2.6 Low
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
EUVDEUVD-2021-0602
matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.
- Record
EUVD-2021-0602- CVSS 3.1
- 2.6 Low
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-52mq-6jcv-j79x
User content sandbox can be confused into opening arbitrary documents
Impact
The user content sandbox can be abused to trick users into opening unexpected documents after several user interactions. The content can be opened with a blob origin from the Matrix client, so it is possible for a malicious document to access user messages and secrets.
Patches
This has been fixed by https://github.com/matrix-org/matrix-react-sdk/pull/5657, which is included in 3.15.0.
Workarounds
There are no known workarounds.
- Record
GHSA-52mq-6jcv-j79x- CVSS 3.1
- 2.6 Low
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
NVD
matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.
- Record
CVE-2021-21320- CVSS 3.1
- 2.6 Low
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N - CVSS 3.1
- 4.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N - CVSS 2.0
- 4.3 Medium
AV:N/AC:M/Au:N/C:N/I:P/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
OSV
matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.
- Record
CVE-2021-21320- CVSS 3.1
- 4.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
OSVGHSA-52mq-6jcv-j79x
User content sandbox can be confused into opening arbitrary documents
Impact
The user content sandbox can be abused to trick users into opening unexpected documents after several user interactions. The content can be opened with a blob origin from the Matrix client, so it is possible for a malicious document to access user messages and secrets.
Patches
This has been fixed by https://github.com/matrix-org/matrix-react-sdk/pull/5657, which is included in 3.15.0.
Workarounds
There are no known workarounds.
- Record
GHSA-52mq-6jcv-j79x- CVSS 3.1
- 2.6 Low
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N - Weakness
- CWE-345
- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
matrix-react-sdknpm |
before 3.15.0 | 3.15.0 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-21320 is a low vulnerability (CVSS 2.6) in Matrix-org Matrix-react-sdk, published March 2, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.92%, the 60th percentile. Fixed in matrix-react-sdk 3.15.0.
References
github.com/matrix-org/matrix-react-sdk/security/advisories/GHSA-52mq-6jcv-j79x
npmjs.com/package/matrix-react-sdk
nvd.nist.gov/vuln/detail/CVE-2021-21320